In general, in optical storage media which are in the form of discs and are suitable for reading from and/or writing the embossed tracks are formed such that they represent an interleaved spiral or concentric circles. Especially in the case of optical storage media which are suitable for writing to, the embossed tracks additionally are wobbled in a specific form, in order to find specific positions on the medium. This means that the track is not embossed in an approximately straight line, but in serpentine lines. By way of example, the shape of these serpentine lines can contain address information which is used to identify a specific position on this optical storage medium. Various methods are used for coding, examples of which include frequency modulation or phase modulation. Furthermore, the wobble signal may also be used for rotation speed information or for presetting a write data rate.
Normally, the modulation shift of this track wobble is kept small, so that there is no noticeable effect on the tracking control and the read quality of the data signal. The modulation shift is thus kept in the order of magnitude of a few percent of the track separation. Furthermore, the modulation frequency is designed to be in a frequency band which is typically above the upper cut-off frequency of the tracking regulator, but is below the lowermost signal frequency of the data signal. However, the small modulation shift means that the signal-to-noise ratio of the wobble signal obtained from it is relatively low. Nevertheless, the coded information and the fundamental frequency should be capable of being coded and reconstructed reliably, in order to allow reliable reading and writing. Disturbance noise components must therefore be effectively suppressed.
U.S. Pat. No. 5,717,679 discloses a system which is able to correct the noise components in the wobble signal resulting from any eccentricity of the wobble track. The circuit which is specified for this purpose uses variable-gain amplifiers in order to compensate for different illumination levels of two detector halves. The system is based on the CD-R technique, which uses a wobble frequency of 22.05 kHz. Since the lowest signal frequency of the data signal is 934 kHz, those data signal components which are likewise present in the wobble signal can easily be removed by means of a low-pass filter, as is also disclosed in U.S. Pat. No. 5,717,679. One disadvantage of this known system is that low-pass filtering is impossible when using wobble frequencies which are close to the lowest signal frequency, as is the case, for example, with DVD technology (wobble frequency 825 kHz). Disturbance data signal components therefore cannot be removed with the disclosed system at high wobble frequencies.
One aim of the invention is to describe a method within an appliance for reading from and/or writing to optical storage media, which can remove disturbance data signal components in the wobble signal even when the wobble frequency and the lowest signal frequency are close to one another.
According to the invention, this object is achieved in that the signals from two detector halves of a photodetector from which a wobble signal is obtained and which is used for reading the data contained in a track of an optical storage medium are provided with weighting factors which are adjusted dynamically during operation of the appliance. In order to adjust the weighting factors, the data signal component in the wobble signal that is obtained is linked to the data signal. Dynamic adjustment of the weighting factors has the advantage that the data signal components in the wobble signal are always suppressed optimally, even if any changes occur in the illumination level of the photodetector during operation.